Cobalt and nitrogen co-embedded onion-like mesoporous carbon vesicles as efficient catalysts for oxygen reduction reaction

A series of cobalt and nitrogen co-embedded onion-like mesoporous carbon vesicles (Co-NMCVs) were synthesized as non-noble metal catalysts for the first time. Physical characterization indicated that the Co-NMCVs samples all retain the lamellar porous shell structure (accompanying considerable surface areas and pore volumes), except the Co20-NMCV sample. Electrochemical measurements demonstrate that most of the Co-NMCV catalysts exhibit remarkable oxygen reduction reaction (ORR) activity in both acidic and alkaline media. Particularly, the Co10-NMCV catalyst exhibits a more positive onset voltage of 0.13 V (only 50 mV deviation from Pt/C), a higher half-wave potential of -0.18 V (only 20 mV deviation from Pt/C), and better selectivity (electron-transfer number >3.92) for the ORR in alkaline medium. Meanwhile, the Co10-NMCV catalyst also shows higher durability of the ORR catalytic activity and better methanol tolerance than the commercial Pt/C catalyst. The unprecedented performance of the Co10-NMCV catalyst in ORR is attributed to the homogeneous distribution of abundant Co-N active sites (having the dominant effect for the ORR catalytic activity) on the surface of the MCV matrix (which has the onion-like lamellar structure, high specific surface area, and large pore volume), which observably enhance the active site density of the Co10-NMCV catalyst. All experimental results demonstrate that the Co10-NMCV catalyst may be exploited as the potentially efficient and inexpensive non-noble metal ORR catalyst to replace Pt-based catalysts.